This invention relates to integrated circuits, and more particularly, to integrated circuits with redundant circuitry.
Integrated circuits are manufactured using complex semiconductor fabrication techniques. One figure of merit when producing integrated circuits is a circuit's manufacturing yield. Circuits that are extremely complex or that are fabricated using cutting-edge processes are generally more difficult to produce without faults than more established circuit designs. As a result, manufacturing yields for newer and more complex circuits are sometimes lower than the manufacturing yields of older designs. Yields can also be negatively affected when designing high performance chips, because devices of this type contain smaller line widths and more complex structures, making them more difficult to manufacture.
Poor manufacturing yields can adversely affect the profitability of an integrated circuit design. In some situations, yields may be so low as to make volume production unfeasible. It is therefore desirable to enhance manufacturing yields whenever possible. This can make otherwise unprofitable integrated circuits economical to manufacture. Enhanced yields can also improve profit margins for integrated circuits that are already profitable.
Although it is beneficial to enhance manufacturing yields whenever possible, it is generally not desirable to do so at the expense of performance or die size. Increases in yield that are achieved through the use of increased die sizes or less aggressive manufacturing techniques may not be acceptable in the marketplace due to issues such as poor power consumption and poor switching speeds.
One way to improve manufacturing yields while maintaining acceptable performance involves providing integrated circuits with redundant circuitry. Following device fabrication, a newly fabricated integrated circuit can be tested. If a defect is detected, circuitry on the device may be reconfigured to bypass the defect. In doing so, spare circuitry can be switched into use in place of the bypassed defect.
This type of redundancy scheme can help to improve manufacturing yields. Devices that would otherwise need to be scrapped can be salvaged and sold to customers. Because the repair process does not adversely affect device performance, repaired devices will operate just as well as devices in which no defects were detected. There are usually a limited number of defects on a given integrated circuit, so it is generally not necessary to provide a large amount of redundant circuitry. Because only a relatively small amount of redundant circuitry is provided, the increased die area and performance penalties associated with providing redundancy are typically outweighed by the considerable economic benefits that result from achieving enhanced manufacturing yields.
Nevertheless, the amount of overhead associated with providing redundancy in modern integrated circuits has been posing challenges. The settings needed to repair a circuit are typically stored in fuses. For example, in a device that has a defective column of memory, the fuses may contain information on which column is defective and may contain settings for bypass switches. As the number of blocks of circuitry on an integrated circuit grows, the number of fuses used to implement this type of redundancy also grows. This, in turn, tends to increase the amount of circuitry used to program and test the fuse settings and increases the amount of routing resources needed to interconnect the fuses with the bypass switches. Overhead issues such as these can make redundancy schemes in complex integrated circuits burdensome.
It would therefore be desirable to be able to provide a redundancy scheme for integrated circuits that addresses these issues and by being efficient in using fuse and routing resources.